Experts dispute how virus spreads
Six months into a pandemic that has killed more than half a million people, more than 200 scientists from around the world are challenging the official view of how the coronavirus spreads.
The World Health Organisation and the US Centres for Disease Control and Prevention maintain that you have to worry about only two types of transmission: inhaling respiratory droplets from an infected person in your immediate vicinity or – less common – touching a contaminated surface and then your eyes, nose or mouth.
But other experts contend that the guidance ignores growing evidence that a third pathway also plays a significant role in contagion. They say multiple studies demonstrate that particles known as aerosols – microscopic versions of standard respiratory droplets – can hang in the air for long periods and float dozens of feet, making poorly ventilated rooms, buses and other confined spaces dangerous, even when people stay 1.8 metres from one another.
‘‘We are 100 per cent sure about this,’’ said Lidia Morawska, a professor of atmospheric sciences and environmental engineering at Queensland University of Technology in Brisbane, Australia.
She makes the case in an open letter to the WHO accusing the United Nations agency of failing to issue appropriate warnings about the risk. A total of 239 researchers from 32 countries signed the letter.
In interviews, experts said that aerosol transmission appears to be the only way to explain several ‘‘super-spreading’’ events, including the infection of diners at a restaurant in China who sat at separate tables and of choir members in Washington state who took precautions during a rehearsal.
WHO officials have acknowledged that the virus can be transmitted through aerosols but say that occurs only during medical procedures such as intubation. CDC officials did not respond to multiple requests for comment.
Dr Benedetta Allegranzi, a top WHO expert on infection prevention and control, said that Morawska and her group presented theories based on laboratory experiments rather than evidence from the field.
‘‘We value and respect their opinions and contributions to this debate,’’ Allegranzi wrote in an email. But in weekly teleconferences, a majority of a group of more than 30 international experts advising the WHO has ‘‘not judged the existing evidence sufficiently convincing to consider airborne transmission as having an important role in Covid-19 spread’’.
Since the coronavirus was first detected in China in December, understanding of how it spreads has evolved considerably, resulting in shifting guidelines regarding the use of masks.
At first, the WHO and CDC said masks were overkill for ordinary people and should be conserved for health workers. Later, the CDC recommended masks only for people with Covid-19 symptoms.
Then in April, after it became clear that people without symptoms could also spread the virus, the CDC suggested masks for everybody when physical distancing was difficult, a position the WHO eventually adopted. – TNS